Hydraulic press



Patented July 18, 1944 UNITED STATES PATENT OFFICE.

2,354,003 HYDRAULIC muss Walter Ernst, Mount Gilead, Ohio, and Don C. Youngblood, Park Ridge, Ill., assignors to The Hydraulic Development Corporation, Inc., Wilmington, Del., a corporation of Delaware Application July 15, 1942, Serial No. 451,066

Claims.

This invention relates to hydraulic machinery and, in particular, to hydraulic presses having a die cushion arrangement for cushioning the pressing operation.

In presses of this type. a material portion of energy was heretofore lost during the cushionblies act on separate draw rings, as is the case in multi-drawing presses, the press platen is additionally subjected to forces which cause the press platen to tilt. 4

Accordingly, it is an object of the invention to provide a press which will overcome the above mentioned drawbacks.

It is another object to provide a press with a fluid operable cushionin device, in which the pressure fluid expelled from said cushioning de-.

vice during the cushioning operation is used for supporting the pressing operation of the press.

Another object of the invention consists in the provision of a hydraulic press having a main plunger and a cushioning cylinder-piston-assembly, in which the main. plunger is associated with auxiliary plunger means adapted to be operated by pressure fluid expelled from said cushioning cylinder-piston-assembly.

It is a further object to provide a press having a plurality of fluid operable cylinder-piston-assemblies, in which pressure fluid expelled from the cushioning cylinder-piston-assemblies, durmg the cushioning operation, is made use of for counteracting the bending forces exerted by the cylinder-piston-assemblies upon the press platen.

These and other objects and advantages of.

the invention will appear more clearly from the following specification in connection with the accompanying drawings. I

This application is a continuation in part application of our copending application, Serial No. 396,892, filed June 6, 1941.

In the drawings:

Figure 1 diagrammatically illustrates a first embodiment of the invention.

Figure 2 is a diagrammatic illustration of the forces acting on the press platen.

Figure 3 is a surge valve, preferably used in connection with the embodiment of Figure 1.

Figure 4 diagrammatically illustrates a further embodiment of the invention.

Figure 5 shows a valve used in connection with the embodiment of Figure 4.

General arrangement The press according to the present invention substantially comprises a main cylinder-pistonassembly associated with auxiliary plungers and adapted to operate a press platen, while a plurality of cushioning plungers is arranged eccentrically with regard to the main cylinder-pistonvassembly for cushioning the pressing operation.

The auxiliary plungers are hydraulically connected with the cushioningplungers so that pressure fluid expelled by the latter during the pressing operation is conveyed to the auxiliary plungers for assisting the main cylinder-piston-assembly in performing a pressing operation.

The cushioning plungers are preferably arranged so', with respect to the auxiliary plungers, that the bending force exerted by the cushioning plungers upon the press platen is substantially balanced by the force exerted by the auxiliary plungers upon said platen.

Structural arrangement of first embodiment Referring to the drawings in detail, the press illustrated in Figure 1 substantially comprises a press head, generally designated l with a main cylinder 2 and auxiliary cylinders 3 and 4.

Reciprocably mounted in the main cylinder 2 is a press ram 5 connected to the press platen 6. Also connected'to the press platen 6 are auxiliary plungers 1 and 8, reciprocabl in the auxiliary cylinders 3 and 4 respectively.

Arranged in the upper portion of the main cylinder 2 is a surge valve 9 connected by conduits I0 and l I with the main cylinder relief and pump by-pass valve I2. The conduit ll communicates with a check valve 16. The surge valve 9 serves the purpose of prefilling the main cylinder 2 during the first portion of the downward stroke of the ram 5, which is effected by gravity, while the main cylinder relief and pump by-pass valve I2 is provided for relieving the pressure in the upper portion of the main cylinder 2 at the initiation of the retraction stroke of the press ram. The surge valve 9 and main cylinder relief and pump by-pass 2 do not form a part of the present invention and for a more detailed description thereof reference may be had to U. S. Patents No.

2,193,248 and No. 2,268,205 to Ernst respectively. Furthermore connected to the valve I2 is a conduit |3 leading to the conduit |4, one end of and I9 are identical and are preferably of the type shown in detail in Figure 3. According to this structure, the surge valve I1 is made up of an upper casing 26 and a lower casing 2|, connected to the casing in any convenient manner. The casing 20 is closed at its upper end by a closure member 22 through which passes the conduit l6.

Reciprocably mounted in the cylinder 23 provided in the casing 20 is a piston 24 connected to a piston rod 25 which passes through a guiding sleeve 26 and is connected to a valve member 21. The valve member 21 controls communication between the bores 28 in the lower casing 2| and the passages 29 communicating with the tank 30 and provided in the upper casing 20. The lower end of the valve casing 2| contains an abutment member 3| against which abuts the lower end of a weak spring 32, the upper end of which engages. the valve member 2'! and urges the latter continuously into closing position. Connected to the surge valve cylinder 23 is a conduit 33'interconnecting the surge valves l1 and I9.

The pump I5 is provided with a servomotor 34 having reciprocably mounted therein a piston 35 connected with the shift ring of the pump and controlling a plurality of ports respectively connected to conduits 36, 31, 38 and 39, and cooperating with two spaced flanges on a valve member 40. The valve member 40 is controlled by the solenoid 4| and continuously urged in one direction by the spring 42.

The conduits Hand 38 lead to a hollow arm 43 connected to the pump 5 and leading to a cylinder in which is reciprocably mounted a piston 44. The piston 44 is connected to th shift ring of the pump and also operatively connected to a threaded rod 45 with a nut abutting against a piston member 46 which, in its turn, abuts one end of a spring 41, the other end of which engages the wall portion of the hollow arm 43.

The conduit 36 communicates with the pressure side of the pilot pump 48 and also communicates with a pressure relief valve 49, which is connected to the conduit 50. One end of the conduit 50 communicates with the tank 30, while the otherend of the conduit communicates with the lower end of the cushioning cylinder 5|. The conduit 50 also comprises a preferably adjustable pressure relief valve 52.

Branching off from'the conduit I6 is a conduit 53 comprising a shutoff valve 54 and a check valve 55, and communicating with. the ch be s 56 and 51 through hollow stationary plungers 58 and 59. The check valve is adapted to be by-passed by a conduit 60 containing a preferably adjustable pressure relief valve 6|. The chambers 56 and 51 are provided in the cushioningv plungers 62 and 63 respectively reciprocable in the cushioning cylinders 5| and 64. The lower end of the cushioning cylinder 64 communicates through conduits 65 and 66 with the tank 30 and the auxiliary cylinder 3 respectively. An adjustable pressure relief valve 61, similar to the relief valve 52, is provided in the conduit 65.

The cushioning plungers 62 and 63 extend through a stationary support 68 which may be a part of the press frame, and which has mounted thereon a lower die 69. The lower die 69 is surrounded by a drawing ring 10 supported by the cushioning plungers 62 and 63 and adapted, in cooperation with an upper die supported by the platen 6, to clamp a work piece 12, when the latter is being drawn by cooperation of the upper die H with the lower die 69.

Operation of first embodiment Assuming that all parts of the press occupy the position shown in Figure 1, while the pumps 48 and I5 are running, and that it is now desired to start a working cycle of the press. To this end, the solenoid 4| is energized in any convenient manner, thereby causing the valve member 40 to move against the thrust of the spring 42. Fluid delivered by the pilot pump 48 then passes through the conduit 36 and the conduit 36 beneath the piston 44 and moves the same upwardly against the thrust of the spring 41, thereby shifting the pump l5 to full delivery forward stroke position.

The shifting movement of the shift ring pertaining to the pump |5 causes the piston 35 also to move upwardly until the shift ring of the pump engages an abutment in the pump casing. It should be noted that the original shifting movement of the pilot valve member 40 is greater than the stroke of the shift ring from neutral position to the position where it engages the said abutme'nt, so that the upper flanged member on the pilot valve member 40 does not fully interrupt communication between the conduits 38 and 36.

Pressure fluid is now delivered by the pump |5 through the conduit |4 into the upper portion of the main cylinder 2, which fluid is supplemented by fluid from the tank 30 passing through the surge valve 9. Fluid from the lower portion of the main cylinder 2 is withdrawn through conduits 13 and I6 to the suction side of the pump IS. The platen 6 now moves downwardly by gravity, carrying with it the auxiliary plungers 1 and 8. This movement causes a suction effect in the auxiliary cylinders 3 and 4, which suction effect acts through the bore 14 (Figure 3) in the abutment member 3| of the surge valves l1 and I9 so as to cause a downward movement of the valve member 21, thereby establishing communication between the tank 30 and the interior of the auxiliary cylinders 3 and 4, and allowing fluid to flow from the tank-30 into the said auxiliary cylinders.

As soon as the upper die 1| engages the work piece 12, pressure builds up in the upper portion of the main cylinder 2, which pressure is conveyed through conduits l4 and 15 into the servomotor 34 where it acts upon the control piston 35 so as to move the latter downwardly, with regard to Figure 1. This downward movement also causes the piston 44 connected to the shift ring piston 24 has moved the valve member 21 of the of the pump to move downwardly. This last mentioned downward movement is possible, since the fluid expelled by the piston 44 may escape through the conduits 38 and 36.

The control piston 35, while moving downwardly, compresses the spring 41, and when the pressure conveyed through conduits l4 and 15 has reached a predetermined value, it moves the piston downwardly to such an extent that the conduit 38 is released and pressure fluid passes from the conduit 15 into the conduit 33 and from there through the conduit 33 into the surge valve cylinder 23 of the surge valves l1 and I8. Here the pressure fluid acts upon the surge valve piston 24, thereby moving the valve member 21 into closing position.

While the platen 6 now continues its downward movement, pressure fluid expelled from the cushioning cylinders 5| and 64 passes through conduits I1 and 66 into the auxiliary cylinders 4 and 3 respectively, where it acts upon the auxiliary plungers 8 and 1, thereby assisting the pressure fluid acting upon the ram 5. Pressure fluid expelled from the chambers 56 and 51 passes through the conduit 66 and the relief valve 6| to the pump I5. Since the pressure fluid expelled from the cushioning cylinders 5| and 64 is conveyed to the auxiliary cylinders 4 and 3 and acts upon the plungers 8 and 1 respectively, a portion of the energy exerted by the platen 6 upon the plungers 62 and 63 is retrieved, and only enough pressure to compensate for the difl'erence between Therefore, a small portion of the fluid expelled from the cushioning cylinders 5| and 64 is passed to the tank 36 through the pressure relief valves Hand 61 respectively.

As will be seen from Figure 1, and particularly from Figure 2 in which the arrows indicate the line and the direction of action of the ram 5 and also of the plungers I, 8, 62 and 63, the plungers I, 8, 62 and 63 are so arranged with respect to each other that the moment exerted upon the platen 6 by the plungers I and 8 equals the mo-v ment exerted by the plungers 62 and 63 upon the said platen. In other words, theforce acting upon the plunger multiplied by 11/2 equals the force acting upon the plunger 62 multiplied by b/2, and the same relationship should prevail between the force acting upon the plunger 8 and the force acting upon the plunger 63.

At the end of the pressing stroke, the solenoid 4| is deenergized by any convenient means, so that the spring 42 moves the pilot valve member 46 downwardly. This establishes hydraulic communication between the conduits 36 and 31 so that fluid from the pilot pump 48 passes through conduit 3'! and, acting upon the piston 44, moves the same downwardly, thereby shifting thepump l5 to full delivery retraction stroke position. As a result, pressure fluid is now delivered into the conduit l6, while the conduit l4 becomes the suction line. i

After the main cylinder relief and pump bypass valve l2 has released the pressure in the upper portion of the main cylinder 2, and the pressure fluid in conduit l6 acting upon the valve surge valves l1 and I8 into its opening position, pressure fluid from conduit l6 passes through conduit 13 and moves the ram 5 upwardly. This movement also causes upward movement of the auxiliary plungers I and 8. Simultaneously, pres-' sure fluid flows through the conduit 53 and the hollow plungers 58 and 58 from the conduit l6 into the plunger chambers 56 and 51 respectively, thereby moving the cushioning plungers 62 and 63 upwardly. f

During this upward movement, the increasing space in the cushioning cylinders 5| and 64 is filled by fluid expelled from the auxiliary cylinders 4 and 3 respectively passing through copduits 1'1 and 66. This fluid is supplemented by fluid from the tank .passing through the surge If desired, the press according to the invention may also be operated without the cushioning cylinderpiston-assemblies. In order to so operate the press, it is merely necessary to close the shutofl valve 54 when the plungers 62 and 63 are in their lowermost position. It will be obvious that,

in this instance, during the entire retraction stroke of the platen 6, the fluid expelled from the auxiliary cylinders 3 and 4 passes through the surge valves l1 and I9 into the tank 38, while the plungers 62 and 63 remain in their lowermost position, since no pressure fluid can enter the chambers 56 and 51 in the cushioning plungers 62 and 63.

Structural arrangement ofsecond embodiment Referring now to Figure 4, the press shown therein is very similar to that of Figure 1, so that a description of the corresponding part appears to be superfluous. To clearly identify these parts, these have been designated with the same reference numerals as the corresponding parts in Fig- The press shown in Figure 4 is a multi-drawing press and may be used so that one pair of dies,

for instance 82, 84, performs a first shaping op-.

eration on a'work piece, while the other pair of dies, in this instance, 83, 85, performs a second drawing step on a work piece which was previously shaped by the dies 82 and 84 and annealed before it was mounted between the dies 83 and 85. A further difference between the embodiment of Figure 4 and the embodiment of Figure 1 con-- sists in the hydraulic circuit associated therewith.

. According to Figure 4, the conduit l4a. communicating with the upper portion of the press cylinder 2a is connected with one side of a variable delivery pump 88, the other end of which communicates through conduits 89 and 90 with a fourway valve, generally designated 9|, and shown in detail in Figure 5. As will be seen from Figure 5, the valve 9| comprises a casing 92 and two chambers 98 and 94 separated by the partition 95. Through this partition passes a shaft of a valve member, generally designated 96. The valve member 98 has a piston 91 reciprocable in the chamber 94 and connected with a smaller piston 98 adapted to be acted upon by pressure fluid conveyed thereto through the conduit 99. The piston 91 controls a port connected to the conduit 90.

The valve member 98 furthermore comprises a piston I controlling a port communicating with a conduit IM and a, piston I 02'contro1ling a port communicating with an exhaust conduit I03. The conduit IOI comprises a check valve I04 and leads into the upper portion of the auxiliary cylinder 30. Similarly, the auxiliary cylinder 4a is connected with a conduit I containing a check valve I08 and leading to the conduit IOI.

Branching off from the conduit IOI is a conduit I01 with an adjustable pressure relief valve I08. The main cylinder relief and pump by-pass valve In is connected with a conduit I09 branching oil from the conduit I4a. Connected to the lower end of the main cylinder 2a is a conduit I I0 leading to the conduit 90 and connected with the conduit I0a.

Connected with the surge tank 30a is a conduit I II containing an adjustable pressure relief valve I I2 and leading to a conduit 'IIa. Branching off from the conduit III is a conduit II3 leading to the servomotor I I4 of the pump 88, while the conduit II5 likewise connected to the servomotor I I4 contains a pressure relief valve IIS and leads to the tank 30a. The pump 88 with the servomotor II4 may be of any conventional design, preferably of the type shown in U. S. Patent No. 2,184,665 to Ernst.

Branching oil from the conduit 99 is the pilot line I I1 comprising the pilot pump 48a and leading to the tank 30a. IAHy excessive pressure created by the pump 48a and prevailing in the conduits II I or H5 is relieved through the pressure relief valve I I8.

The conduit 90 communicating with the hollow plungers 58a and 59a comprises a shutofl. valve 54a and a check valve 55a. Furthermore connected with the conduit 90 is a normally closed valve I I8, which opens in response to a predetermined fluid pressure acting thereupon, and is connected through the conduit II9 with the conduit I 4a. The conduit 90 is also connected with a conduit I20 comprising an adjustable pressure relief valve I2,I and leading to the conduit 88a.

Operation of second embodiment Assuming that all parts of the press occupy the position shown in Figure 4, and that the pumps 88 and 48a are running, the operator, in order to start a working cycle, shifts the pump 88 in any convenient manner so that pressure fluid is delivered by the pump 88 into the conduit I4a. From the conduit I4a fluid passes into the upper portion of the main cylinder 2a, while fluid is withdrawn from the lower portion of the main cylinder 2a through the conduit H0 and returned to the suction side of the pump 88 through the conduit 89. While the ram So now moves downwardly by gravity, fluid delivered by the pump 88 into the maincylinder 2a is sup- 78 plemented by fluid from the tank 30a passing through the surge valve 9a.

Downward movement of the ram 5a and, thereby of the platen to, causes the plungers Ia and 8a, connected to the platen So, also to move downwardly. This movement creates a suction effect in the auxiliary cylinders 3a and 4a with the result that the check valves I22 and I23 admit fluid from the tank 30a into the auxiliary cylinders 3a' and 4a respectively.

The operation of the pilot pump 48a causes fluid to pass through conduits II I and H5 and the pilot line 99 into the four-way valve 92, where it acts .upon the piston 98 and moves the valve member 98 to its left hand position. In this position, the ports respectively connected to? the conduits 90 and I03 are closed.

As soon as one of the upper dies 84, engages the respective work piece 88 or 81, pressure starts to build up in the upper portion of the main cylinder 2a with the result that the surge valve 9a closes. When the respective die 84 or 85 starts its actual pressing operation, the cushioning plunger pertaining thereto begins to move downwardly, thereby expelling pressure fluid from the respective cushioning cylinder into the auxiliary cylinder connected thereto.

According to the showing of Figure 4, the drawing rings 18 and 19 are so arranged with respect to each other that the work pieces 86 and 81 are engaged by the respective dies at approximately one and the same time, but it is of course understood that this is by no means necessary. It will be clear that when both dies 84 and 85 act upon the respective work pieces, pressure fluid from both cushioning cylinders 84a and 5| a will be conveyed to the auxiliary cylinders-3a and 4a. The pressure fluid thus conveyed to the auxiliary cylinders acts upon the plungers Ia and 8a respectively, which in their turn assist in the pressing operation of the ram 5a. In this way, a portion of the energy exerted by the platen 6 upon the cushioning plungers 63a and 82a is retrieved, and only enough pressure to compensate for the difference between the effective areas of the cushioning plungers on one hand, and the effective 'areas of the auxiliary plungers 8a and la must be supplied to the ram 5a in addition to the force required to keep the platen 8a in motion.

Also in this arrangement the distance between the axes of the auxiliary plungers 1a, 8a and the axis of the ram 50, and the distance between the axes of the cushioning plungers 82a, 83a and the axis. of the ram 5a is such that the forces exerted upon the platen 6a by the auxiliary plungers is approximately balanced by the forces exerted upon the platen' Go by the cushioning plungers 83a and 82a. In this way, the forces tending to bend the platen and to tilt the latter are reduced to a. minimum. This is of particular importance in connection with multi-drawing presses of the type shown in Figure 4, in which, as a rule, the work piece subjected to the second shaping operation offers a greater resistance than the work piece simultaneously subjected to the first shaping operation.

It will be appreciated from the above that if for instance the work piece 81, during its drawing operation, exerts a greater resistance upon the platen 811 than the work piece 88, the pressure fluid conveyed from the cushioning cylinder 5Ia to the auxiliary plunger 8a will be higher than the pressure of the pressure fluid conveyed from the cushioning cylinder 84a to the auxiliary plunger 1a so that, as a result, the press ram will press is operated with one cushioning cy1lnderpiston-assembly only, while the other cushioning cylinder-piston-assembly is ineffective. The press platen now performs its pressing stroke in the usual manner.

At the end of the pressing stroke, or when a predetermined pressure has been built up in the main cylinder 2a, means, well known to those skilled in the art, actuates the servomotor H4 50 as to cause movement of the pump 88 from its forward stroke position to full delivery retraction stroke position. As a result thereof, the pump 88 now delivers pressure fluid through conduits 89 and 98 on one hand into the valve chamber 94 and on the other hand through conduits I24 and I25 into the chambers 56a and 51a of the cushioning plungers 62a and 63a.

Pressure fluid delivered into the chamber 94 acts upon the valve piston 81 and moves the valve member 96 toward the right with regard to Figure against the pressure acting upon the valve plunger 88 by the constant low pressure pump 48a. Rightward movement of the valve member 86 establishes communication between th conduits II and I03.

Delivery of pressure fluid from the pump 88 into the chambers 56a and 51a initiates upward movement of the plunger 62a and 63a. Simultaneously, pressure fluid is delivered by the pump 88 through conduits 90 and III! into th lower Portion of the main cylinder 2a, thereby initiating the upward movement of the ram 5a and the platen 6a,-connected thereto. At this time, the surge valve 9a is open.

While the platen 6a and the auxiliary plungers Ia and 8a, as well as the cushioning plungers 62a and 63a, move upwardly, fluid expelled from the cylinders 3a and 4a passes through conduits 11a and 66a into the cushioning cylinders 5Ia and 64a respectively. This fluid is supplemented by fluid flowing from the tank 30a through the check valves I23 and I22 into the conduit 'IIa and 660 respectively. Fluid expelledfroin the upper portion of the main cylinder 2a passes through the surge valve 911 into the tank 30a.

When the cushioning plungers 62a and 63a have reached the upper end of their stroke, they come to a standstill, while the platen 8a still continues its upward movement, thereby stripping the work pieces from the upper die. During this last portion of the retraction stroke of the platen 6a, the fluid expelled by the plungers Ia and 8a passes through the check valves I III and I 06 and the conduit I BI into the valve chamber 93, from where it flows through the exhaust conduit I03 7 into the tank 30a.

When the platen Ed has reached the end of its retraction stroke, the pump 88 is moved to neutral or no delivery position by any convenient means, thereby stopping the press which is now ready for anew cycle.

Also the structure of Figure 4, 11? desired, may

be operated without actuating the cushioning" hend within our invention such modifications as come within the scope of the claimsand the invention.

Having thus fully described our invention, what we claim as new and desire to secure by Letters Patent is:

1. In a press having a platen and fluid operable cushion means cooperating with said platen to cushion the pressing action thereof, hydraulic motor means operatively connected with said platen for advancing the same including main and auxiliary cylinder-piston-assemblies, and means connected with said cushion means for conveying pressure fluid expelled by said cushion means to the auxiliary cylinder-pi'ston-asseinbly of said motor means for aiding the same in advancing said platen.

2. In a press having a platen and fluid operable cushion means cooperating with said platen to cushion the pressing action thereof, a main cylinder-piston-assembly operable by pressure fluid for actuating said platen, an auxiliary cylinder-piston-assembly associated'with said main cylinder-piston-assembly and operable to assist said main cylinder-piston-assembly in advancing said platen, and means responsive to the pressing action of said platen for conveying pressure fluid from said cushion means to said auxiliary cylinder-piston-assembly. I

3. In combination in a press having a platen and a fluid operable main cylinder-piston-assembly for actuating said platen; a plurality of cushion cylinder-piston-assemblies for supporting a work piece, each cylinder of said cushion cylinder-piston-assembly being arranged to receive fluid adapted to be subjected to pressure by said platen, a plurality of auxiliary cylinder-pistonassemblies operable to exert advancingforce on said platen, each of said cushion cylinder-pistonassemblies having associated therewith an auxiliary cylinder-piston-assembly, and means responsive to the pressing operation of said platen for conveying pressure fluid from said cushion cylinder-piston-assemblies to said auxiliary cylinder-piston-assemblies for actuating the latter.

4. In a press having a platen and a fluid opioning cylinder, an auxiliary fluid operable motor I operable to assist said main cylinder-piston-assembly in advancing said platen, conduit means continuously interconnecting said cushioning cylinder and said auxiliary motor, and means responsive to a predetermined pressure in said main cylinder-piston-assembly for controlling hydraulic connection between said booster cylinder and an exhaust.

5. In combination in a press havinga press platen and a fluid operable main cylinder-piston-assembly for actuating said platen, a plurality of cushion cylinder-piston-assemblies arranged to be supplied with fluid adapted to be subjected to pressure by said platen, a plurality of auxiliary eylinder-piston-assemblie corresponding in number to said cushion cylinder-piston-assemblies and operable to exert advancing force on said platen, means responsive to a predetermined pressure in said cushion cylinderpiston-assemblies for conveying pressure fluid therefrom to said; auxiliary cylinder-piston-assemblies, a reversible variable delivery pump for supplying pressurefluid to said main cylinderpiston-assembly, surge valve means associated with said auxiliary cylinder-piston-assemblies and responsive to a suction effect therein for admitting fluid from a fluid source to said auxiliary cylinder-piston-assemblies, and means associated with said surge valve means and responsive to a predetermined pressure in said main cylinderpiston-assembly for positively closing said surge valve means.

6. In combination in a press having a press platen and a fluid operable main cylinder-pistonassembly for actuating said platen, a plurality of cushion cylinder-piston-assemblies adapted to be supplied with fluid, said platen being arranged to creat fluid pressure in said cushion cylinder-piston-assemblies, a plurality of auxiliary cylinderpiston-assemblies operable to exert advancing force on said platen, each of said cushion cylinderpiston-assemblie' having associated therewith an auxiliary cylinder-piston-assembly, means responsive to a predetermined pressure in each of said cushion cylinder-piston-asseinblies for admitting pressure fluid to the respective auxiliary 'cylinder-piston-assembly, a reversible variable delivery pump for supplying pressure fluid to said main cylinder-piston-assembly, surge valve means associated with 1 said auxiliary cylinderpiston-assemblies and responsive to a suction effect therein for admitting fluid from a fluid source to said auxiliary cylinder-,piston-assemblies, and means associated with said variable delivery pump and responsive to a predetermined pressure on the pressure side thereof for conveying said pressure to said surge valve means to close the latter.

'7. In a press having a platen and a fluid operable main cylinder-piston-assembly for actuating said platen, a plurality of cushion means adapted to cushion the action of said platen, a plurality of auxiliary cylinder-piston-assemblies operable to exert advancing force on said platen, means for hydraulically connecting each of said cushion means with an auxiliary cylinder-pistonassembly, means responsive to thepressing operation of said platen for conveying pressure fluid from said cushion means to said auxiliary cylinder-piston-assemblies to assist the advancing force of said main cylinder-piston-assembly, valve means responsive to the initial advancing movement of said main cylinder-piston-assembly for admitting fluid to said auxiliary cylinder-piston-assemblies, and additional valve means responsive to the retraction movement of said main cylinder-piston-assembly for enabling fluid in said auxiliary cylinder-piston-assemblies to escape to an exhaust.

8. In a hydraulic press having a fluid operable main pressing plunger operatively connected with a press platen, a plurality of fluid operable auxiliary plungers arranged laterally of said main plunger and connected with said platen for assisting the advancing movement of said main plunger, and a plurality of cushioning plungers for cushioning the advancing movement, of said main plunger, th longitudinal axis of each cushioning plunger being located between the axis of an auxiliary. plunger and the axis of said main pressing plunger so that the bending force exerted by said cushioning plungers on said platen is substantially balanced by the bending force exerted by said auxiliary plungers on said platen.

9. In a hydraulic press having a fluid operable main pressing plunger operatively connected with a press platen, a plurality of fluid operable auxiliary plungers arranged laterally of said main plunger and connected with said platen for exerting an advancing force thereon, a plurality of cushioning plungers corresponding in number to that of said auxiliary plungers and having an effective plunger area larger than the effective plunger area ofsaid auxiliary plungers, the longitudinal axis of each cushioning plunger being located between the axis of said main plunger and the axis of an auxiliary plunger so that the bending forces exerted by the cushioning plungers on said platen are substantially balanced by the bending force exerted by the auxiliary plungers on said platen, and conduit means hydraulically connecting each cushioning plunger with its ad- Jacent auxiliary plunger to allow transfer of pressure fluid from each cushioning plunger to its adjacent auxiliary plunger.

10. In a hydraulic apparatus. having a main plunger operatively connected with a press platen for actuating the same, a pair of cushioning plungers respectively located on opposite sides with regard to the axis of said main plunger for action on one side of said platen, a pair of auxiliary plungers located on opposite sides of said main plunger and'having a piston area smaller than the piston area of said cushioning plungers for action on the opposite side of said platen, the distance between the axes of said auxiliary plungers being greater than the distance between the axes of said cushioning plungers so that the bending forces exerted by said auxiliary plungers on said platen are substantially balanced by the bending forces exerted by said cushioning plungers on said platen, and means for hydraulically interconnecting each cushioning plunger with the adjacent auxiliary plunger to allow transfer of pressure fluid from the former to the latter during the advancing movement of said platen.

WALTER ERNST. DON C. YOUNG-BLOOD. 

